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Bizarre hexagon circles Saturn’s north pole

A six-sided feature spanning 25,000 kilometres circles Saturn’s north pole in this infrared image taken by Cassini

(Image: NASA/JPL/U Arizona)

An auroral ring (blue) adorns this image of the hexagon above Saturn’s north pole, taken on 29 October 2006 from a distance of about 905,000 kilometres above the clouds

(Image: NASA/JPL/U Arizona)

A hurricane-like vortex swirls on Saturn’s south pole, where towering clouds cast shadows around them

(Image: NASA/JPL/Space Science Institute)

A deep, hexagon-shaped feature lies above Saturn’s north pole, newly released images from the Cassini spacecraft reveal. The strange structure appears to be nearly stationary and may be a wave that stretches deep into the giant planet’s atmosphere.

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NASA’s Voyager 1 and 2 spacecraft glimpsed parts of the feature nearly 30 years ago, but because of their viewing angle, they were not able to see the whole thing. Now, Cassini’s visual and infrared mapping spectrometer has captured the entire hexagon for the first time, thanks to a series of infrared images it took as the spacecraft flew over the pole in October and November 2006 (see Cassini snaps Saturn from a dizzying height).

“This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides,” says team member Kevin Baines of NASA’s Jet Propulsion Laboratory in Pasadena, California, US. “We’ve never seen anything like this on any other planet.”

Striking differences

In a statement, NASA says the feature may be “an unusually strong pole-encircling planetary wave that extends deep into the atmosphere”.

“It’s amazing to see such striking differences on opposite ends of Saturn’s poles,” says Bob Brown, leader of the Cassini visual and infrared mapping spectrometer at the University of Arizona in Tucson, US. “At the south pole, we have what appears to be a hurricane with a giant eye, and at the north pole of Saturn we have this geometric feature, which is completely different.”

Currently, the hexagon can only be detected at infrared wavelengths because it is winter in the northern hemisphere – a 15-year-long season in which sunlight does not fall on the pole. As spring begins to dawn in the region over the next two years, astronomers will search for the feature at visible wavelengths.